Project Summary: Applying methods advocated by OMERACT (Outcome Measures in Rheumatology), this application will use a data-driven, consensus approach to develop a fibromyalgia response index that will incorporate information from several outcome measures into a single definition of improvement. This responder index will have the potential to greatly enhance the comparability, validity, and clinical applicability of fibromyalgia trials. The development of a fibromyalgia responder index will involve the following steps: 1) Selection of outcome measures based on consensus about key symptom domains for fibromyalgia trials and assessment of the measures using existing databases from recently completed pharmacological fibromyalgia trials;2) Use of the core set of outcome measures to test several different definitions of fibromyalgia state (i.e., level of activity of the illness) and improvement. A clinician survey will be conducted to assess the possible definitions that best correspond to the clinical impression of the patient fibromyalgia activity and improvement with intervention. The definitions of improvement will be tested using existing pharmacological datasets;and 3) Presentation of evidence to OMERACT, with the intention of seeking consensus on the fibromyalgia responder index. Since there are no clinician-rated instruments that assess symptom domains of fibromyalgia, a secondary Aim of the project is to compare clinician ratings (using a newly developed instrument, the Fibromyalgia Rating Scale) with patient ratings to determine whether clinician assessments might add important information to a responder index. Relevance: Although fibromyalgia causes substantial morbidity and disability, there are few proven effective treatments and no U.S. Food and Drug Administration (FDA)-approved treatments. Advances in the treatment of fibromyalgia have been impeded by the absence of consensus about either a core set of outcome measures or a definition of clinically meaningful response to treatment in fibromyalgia trials. The development of a single definition of response in fibromyalgia trials is important for the advancement of the treatment of fibromyalgia and establishment of an FDA-approved treatment.